1. Field of the Invention
The present invention generally relates to the switching of nodes constituting a cluster system.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication 2006-260357 or the like is known as a conventional technique relating to a node for controlling access to a storage device. In Japanese Unexamined Patent Application Publication 2006-260357, a plurality of nodes are provided in the form of a cluster system to respond to the occurrence of a fault in a node. In the cluster system, one of the plurality of nodes serves as an active system node for controlling access to a storage device, and the other nodes serve as standby system nodes that remain on standby until a fault occurs in the active system node. Thus, when a fault occurs in the active system node, one of the standby system nodes serves as the active system node in place of the faulty node, and as a result, access to the storage device can be controlled.
In a typical cluster system, node switching upon the occurrence of a fault is performed in accordance with a pre-defined node order. Hence, when a fault also occurs in a standby system node, node switching may be performed meaninglessly.
For example, in a case where a cluster system is constituted by four nodes (node 1, node 2, node 3, node 4) and the order thereof is defined as node 1→node 2→node 3→node 4, when no fault occurs, the first node in the node order, i.e. node 1, serves as the active system node and the other nodes, i.e. node 2, node 3, and node 4, serve as standby system nodes. Then, when a fault occurs in node 1, the standby system node having the highest order, i.e. node 2, is switched to become the active system node. Here, when a fault also occurs in node 2, further node switching is performed such that node 3, which follows node 2 in the node order, is switched to become the active system node. In other words, when a fault occurs in node 1 and a fault also occurs in node 2, the switch from node 1 to node 2 is meaningless. When meaningless switching is performed in this manner, an excessive amount of time is required for normal access to the storage device to become possible.